As mentioned,, American Holly wood is about as close to real ivory you can get w/o actually getting ivory.
As for which grip frame,, fits which stocks,, well, remove the factory stocks,, and check the grip frame for markings. It'll tell you which ones are correct. However,,, realize that the newest Rugers will have the infernal,,, eeerrr internal lock assy that any stocks have to be hollowed out for.
I know,, as I made 4 sets of stocks for my 2 45 Colt New Vaqueros,, and my pair of Lipseys 44 spls.